Index: Objects/stringlib/formatter.h
===================================================================
--- Objects/stringlib/formatter.h	(revision 83227)
+++ Objects/stringlib/formatter.h	(working copy)
@@ -1136,9 +1136,10 @@
         /* Omitted type specifier. Should be like str(self). */
         type = 'g';
         default_precision = PyFloat_STR_PRECISION;
-        add_parens = 1;
-        if (re == 0.0)
+        if (re == 0.0 && copysign(1.0, re) == 1.0)
             skip_re = 1;
+        else
+            add_parens = 1;
     }
 
     if (type == 'n')
@@ -1223,8 +1224,11 @@
                                     n_re_digits, n_re_remainder,
                                     re_has_decimal, &locale, &tmp_format);
 
-    /* Same formatting, but always include a sign. */
-    tmp_format.sign = '+';
+    /* Same formatting, but always include a sign, unless the real part is
+     * going to be omitted, in which case we use whatever sign convention was
+     * requested by the original format. */
+    if (!skip_re)
+        tmp_format.sign = '+';
     n_im_total = calc_number_widths(&im_spec, 0, im_sign_char, p_im,
                                     n_im_digits, n_im_remainder,
                                     im_has_decimal, &locale, &tmp_format);
Index: Lib/test/test_complex.py
===================================================================
--- Lib/test/test_complex.py	(revision 83227)
+++ Lib/test/test_complex.py	(working copy)
@@ -506,6 +506,16 @@
         self.assertEqual(format(z, '-'), str(z))
         self.assertEqual(format(z, '<'), str(z))
         self.assertEqual(format(z, '10'), str(z))
+        z = complex(0.0, 3.0)
+        self.assertEqual(format(z, ''), str(z))
+        self.assertEqual(format(z, '-'), str(z))
+        self.assertEqual(format(z, '<'), str(z))
+        self.assertEqual(format(z, '2'), str(z))
+        z = complex(-0.0, 2.0)
+        self.assertEqual(format(z, ''), str(z))
+        self.assertEqual(format(z, '-'), str(z))
+        self.assertEqual(format(z, '<'), str(z))
+        self.assertEqual(format(z, '3'), str(z))
 
         self.assertEqual(format(1+3j, 'g'), '1+3j')
         self.assertEqual(format(3j, 'g'), '0+3j')